For the work you've described, any of these cameras will do. And before you go dropping $8000 on that three pound brick otherwsie known as a D3X...You do realize you've still got to buy at least one lens unless you already own a Nikon compatible lens, right? The camera doesn't matter as much as how your use and control composition and lighting. The only way to easily tell what camera was used to take a photo is to see the EXIF data in the file or otherwise recorded by the photographer.
Another note on the lens: Your choice of lens often matters more than you choice of cameras because one often can tell the difference between a photo taken with cheap glass versus the same scene shot with really sharp, high quality glass just by looking at the photo. This becomes especially important if you intend to enlarge the final image to anything beyond a 5x7 print. The lens may even determine whether or not the shot you want is even possible.
It is worth noting tha all of these cameras have the same basic photographic controls. They all offer (M) manual, (A) aperture priority, (S) shutter priority, and (P) programmed exposure modes with +/- 5 stops of exposure compensation. Everthing from the D90 down has a maximum shutter speed of 1/4000th of a second at up to 4.5 frames per second in the D90. Everything from the D300 to the D3X offers a top shutter speed of 1/8000th of a second at anywhere from five (D700) to eleven (D3) frames per second. The higher end Nikons also offer better build quality and more dedicated buttons/switches. These features become important if you shoot in inclement weather or need to adjust metering modes, exposure compensation or other settings more quickly than you might on the lower-end, entry level cameras. Everything from D90 on up in Nikon's line provides autofocus and metering with all but two Nikon F3AF lenses. Lower-end Nikons can only autofocus with AF-s or AF-i lenses but otherwise offer most of the same lens compatibility as the larger camera.
Whether you need the high-end Nikons really depends on whether you need the features and capabilities all that extra money affords you. Many professionals and advanced amatuers do find use for them. But if you don't plan to do much in the way of photo editing, save your money and buy a D3000 (replaces the D40 and D60) and put the rest of your budget toward better lenses. Master the core skills of photography with the D3000 and you'll be able to make a competent decision about what lenses and cameras to buy later. You'll also know by then that Yahoo Answers is not the best place for information on cameras.